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Old Army flashlight updated to modern technology

When I was very, very young, my parents gave me an old Army flashlight, made ~1963. It was, I'm pretty sure, the first light I ever owned. On a visit this past summer, I was asked by my mother to go through the bicycles that came out of the tool shed my parents had removed, and identify which I wanted to keep for my own children and which she could give away. (In my youth, I was as big a bicycle nut as I am a flashlight nut now, and had a collection of at least 5 bicycles that I kept in rotation.) Before I could even begin to get nostalgic about seeing my main/favorite bike for the first time in ~20 years, I spotted that old flashlight. It was an Army Green, 2 D-cell, L-shaped light. Ther were probably millions made - a real dime-a-dozen... but not to me. To me, it was the one that gave way to a fascination that lay dormant in me for several decades and then lit up like wildfire. It sat on my shelf for several months until today, when it visited my workbench for some updating...

The 2-cell bulb, reflector, and plastic lens have been replaced with a glass lens and homemade light engine utilizing a 4000K high CRI CREE XP-G and MOP Aluminum reflector:

The LED is driven by two DX 25505 boost drivers wired to run in parallel and modified by adding R100 sense resistors to each of them to boost output current. Total output on fresh Alkalines or NiMH cells is ~1.8A to the LED. Current draw at the tail can be as high as 4.1A on NiMH and nearly that on fresh D primaries.

As long as it's being modernized, I thought I'd add some glow (rings that is):

And to demonstrate the success, here are the requisite beamshots...

First, with the flash enabled to demonstrate the warm tint of the LED (vs. the cold strobe of the flash):

And without flash:

With the exception of an old 6V lantern, whose battery just won't die, this will be the only other light I keep Alkaline batteries in, mainly out of nostalgia.

I'm sorry I didn't take before and after beamshots after cleaning up the switch with 2-26 contact cleaner but before modding the rest. When I first turned it on after I cleaned the switch, I didn't think it was working until I turned it around and looked directly at the bulb. Kestrel was kind enough to provide this reference beamshot, which you can imagine as a before-shot (although I don't think this light was working even quite that well.):

Last edited by Techjunkie; 02-17-2012 at 12:35 PM.
Reason: before/ref pic added to end

Re: Old Army flashlight updated to modern technology

Originally Posted by Techjunkie

I'm sorry I didn't take before and after beamshots after cleaning up the switch with 2-26 contact cleaner but before modding the rest. When I first turned it on after I cleaned the switch, I didn't think it was working until I turned it around and looked directly at the bulb.

Re: Old Army flashlight updated to modern technology

Looks nice, older lights like those always have a sedimental value especially if it was one of your first lights. Hows the heat buildup?

The heat is absorbed very well into the mass of the heavy brass base and then into the heavy aluminum reflector it screws into. From there, with the light being made of plastic, the thermal path really slows down, I imagine. Some of that heat escapes through the glass lens (which makes direct contact with the reflector) and some through metal switch via the sheet metal conduit,but it's total thermal resistance from LED to air is probably a fraction of what it would be if the host were all metal. I've run it for ~5 minutes and not noticed any dimming or blue-ing of the light, but I haven't been brave enough to let 'er rip for an extended runtime (besides, D batteries are expensive).

Re: Old Army flashlight updated to modern technology

In response to this thread, someone asked me by PM what other LEDs could be used when modding a light like this. Before I knew it, I was writing a dissertation on flashlight modding in general. For the benefit of future reference, I'm posting my reply here for all to see. What follows is the "Cliff's Notes" version of what I've learned at CPF on the topic:

Your LED selection should be based on several factors. Each factor becomes even more relevant when constructing a single-mode / single-purpose flashlight.

Your battery selection - what's the capacity, what's the current/discharge capability, how much will Vout sag under load?

How you intend to use the light - long runs or short bursts? Does total runtime between battery recharge-or-replace matter?

Heatsinking capability. This can trump all other factors, especially when building a "wow" light.

Beam pattern/profile desired - narrow or wide

Obviously, if the light were built with multiple mode capability, then different modes would reduce the impact of all the factors above.

1. Batteries:

Alkalines: These have great capacity and long shelf life due to low self discharge rate. Current capability is low and voltage drops significantly as the cell discharges its supply and its remaining capacity lessens. For that reason, Alkalines are used most effectively with high output LEDs when there are four or more of them and a buck driver (DC-DC converter with constant current output, where V.in is greater than V.out) is used. D-Cells can provide considerably more current (amps) than smaller cells, although as with all alkalines, maximum current capability lessens as remaining capacity lessens. For that reason, 2 D cells, with their enormous capacity, can drive a high power LED fairly well using boost drivers (DC-DC converter with constant current output where V.in is less than V.out). Output will wane as the cells lose capacity. Circuit limitations on the maximum current that can be input into the boost driver by the cells will cause output to wane when cell voltage drops to a point that the maximum input current required to achieve the target output current is exceeded.

NiMH rechargeables: These are no charging-memory-effect, 1:1 replacements for Alkalines. Self discharge rate is high, with the exception of the special Low Self Discharge (LSD) variety of NiMH cell. Nominal cell voltage is 1.2V. V.out over the entire discharge is very flat compared to alkalines. Sag under load is far less than that of alkalines. Among the variety of NiMH Cells, lower capacity cells tend to have lower internal resistance and are typically capable of providing higher current with less sag. Among the most commonly available cells, the best for being LSD with high current capability are Sanyo Eneloops and the white-topped, Japanese made Duracell Precharged NiMH.

Conventional (LiCo chemistry) Li-Ion rechargeables: These have enormous capacity and very low self discharge rate (lower than LSD NiMH). Their maximum safe current discharge capability in mA is typically 2-3x their capacity in mAH. Exceeding that maximum safe limit is VERY dangerous. These are the cells that catch fire and explode if shorted, crushed, punctured, highly over charged, highly over discharged. Protection circuits offer some protection in the form of preventing overcharge, overdischarge and short circuit. Not all Li-Ion cells have protection circuits. Excessive discharge current, overcharge, discharge all damage the cell, increasing its internal resistance and lessening its capacity. As with all Li-Ion chemistry, good chargers that prevent damage to the cell by varying charging rate based on resistance and cut off charge at 4.20V are expensive. Many cheap chargers exist that rely on the cell's protection circuit to cut off charge at 4.20v and should be avoided, should a protection ciruit fail or should you ever with to use unprotected, safer chemistry 3.6-3.8V cells. The nominal voltage of these cells is slightly higher than V.in of a white LED, making them ideal for 1 cell flashlights with current regulators, or 2 (or more) cell lights with buck drivers.

IMR cells (Li-Ion rechargeables of different chemistry, usually LiMn or other Li + Mn chemistries): These are the "safe chemistry" Li-Ion rechargeables that are much more stable because of the way oxygen liberation is avoided in the chemistry. Capacity is less than that of conventional LiCo chemistry Li-Ion cells. Nominal voltage is 3.7-3.8v. Maximum safe discharge current in mA is typically 5x capacity in mAH. Lack of protection circuits on these cells requires a good charger. Over charge, over discharge and excessive discharge current will damage these cells by increasing internal resistance and reducing capacity. Best brand available as loose cells is AW IMR. Other brands typically found in tool packs, such as Molicell, are sometimes available as loose cells.

LiFePO4 cells: Safest Li chemistry. Lowest capacity. No protection circuits. Nominal voltage 3.2V. Maximum safe discharge current varies with brand but is almost always at east 5x capacity and sometimes as high as 20x capacity. As with other chemistries, the highest current capable cells typically have the lowest capacity. These cells handle abuse better than any other Li chemistry, especially rebounding from over discharge. Maximum number of recharge cycles is twice that of LiCo and LiMn cells. Best brand is A123 Li Nano Phosphate cells. Inexpensive, unbranded LiFe cells from China are widely available as loose cells. A special 3.0/3.2v cell charger with cutoff is required to avoid overcharging.

2. Intended purpose or use of the light:
Single mode lights don't have the benefit of having a low mode for long runtime and a high mode for short burts. If extended runs are desired, then choosing an emitter and a drive current for it will have to consider heatsinking and heat shedding, as well as the total desired runtime on a single charge or single set of batteries. Desire for long total runtime and/or heatshedding limitations will reduce max LED wattage that's appropriate for the light.

3. Heatsinking / Heat shedding capability:
If the light needs to be capable of being left on for extended periods, then heatsinking is very important. Heatsinks protect LEDs from thermal runaway by absorbing and then shedding heat from the LED. If the sink can't shed the heat to the environment through the host as fast as it can absorb it from the LED, then total Wattage should be limited to maximize runtime before the sink is soaked and throttling or runaway occurs.
Plastic lights have a heatsinking handicap. No running big giant emitters (XML,SST50,SST90) at full blast, at least not for more than just 1-2 minutes. You can run an XPG at full blast in short bursts until the sink is soaked. As heatsink mass increases, the amount of heat it can store before being soaked (temperature = LED runaway temp) increases.

4. Desired beam profile:
The other factor to consider is the type of beam profile you want. Do you want a narrow, focused beam that concentrates most of the light for throw, or do you want a flood light for close-range use that lights up a wide area nearby? In a fixed focus reflector, and with fairly constant power and heat profiles (i.e. same wattage as driven), a small emitter driven hard will produce better throw and a more intense hotspot, and a larger emitter will produce brighter flood and a softer hotspot.

Re: Old Army flashlight updated to modern technology

Nice job, as usual, Techjunkie! Back in September I put an XM-L in a yellow and black plastic Rayovac flashlight with a rebel reflector an homemade heat sink. The light does not have sentimental value like yours, but it is a real sleeper! Keep up the innovative builds!

Re: Old Army flashlight updated to modern technology

...... a dissertation on flashlight modding in general. ...... What follows is the "Cliff's Notes" version of what I've learned at CPF on the topic:

Your LED selection should be based on several factors. Each factor becomes even more relevant when constructing a single-mode / single-purpose flashlight.

Your battery selection - what's the capacity, what's the current/discharge capability, how much will Volt sag under load?

How you intend to use the light - long runs or short bursts? Does total runtime between battery recharge-or-replace matter?

Heatsinking capability. This can trump all other factors, especially when building a "wow" light.

Beam pattern/profile desired - narrow or wide

Obviously, if the light were built with multiple mode capability, then different modes would reduce the impact of all the factors above.

1. Batteries:

Alkalines: These have great capacity and long shelf life due to low self discharge rate. Current capability is low and voltage drops significantly as the cell discharges its supply and its remaining capacity lessens. For that reason, Alkalines are used most effectively with high output LEDs when there are four or more of them and a buck driver (DC-DC converter with constant current output, where V.in is greater than V.out) is used. D-Cells can provide considerably more current (amps) than smaller cells, although as with all alkalines, maximum current capability lessens as remaining capacity lessens. For that reason, 2 D cells, with their enormous capacity, can drive a high power LED fairly well using boost drivers (DC-DC converter with constant current output where V.in is less than V.out). Output will wane as the cells lose capacity. Circuit limitations on the maximum current that can be input into the boost driver by the cells will cause output to wane when cell voltage drops to a point that the maximum input current required to achieve the target output current is exceeded.

NiMH rechargeables: These are no charging-memory-effect, 1:1 replacements for Alkalines. Self discharge rate is high, with the exception of the special Low Self Discharge (LSD) variety of NiMH cell. Nominal cell voltage is 1.2V. V.out over the entire discharge is very flat compared to alkalines. Sag under load is far less than that of alkalines. Among the variety of NiMH Cells, lower capacity cells tend to have lower internal resistance and are typically capable of providing higher current with less sag. Among the most commonly available cells, the best for being LSD with high current capability are Sanyo Eneloops and the white-topped, Japanese made Duracell Precharged NiMH.

Conventional (LiCo chemistry) Li-Ion rechargeables: These have enormous capacity and very low self discharge rate (lower than LSD NiMH). Their maximum safe current discharge capability in mA is typically 2-3x their capacity in mAH. Exceeding that maximum safe limit is VERY dangerous. These are the cells that catch fire and explode if shorted, crushed, punctured, highly over charged, highly over discharged. Protection circuits offer some protection in the form of preventing overcharge, overdischarge and short circuit. Not all Li-Ion cells have protection circuits. Excessive discharge current, overcharge, discharge all damage the cell, increasing its internal resistance and lessening its capacity. As with all Li-Ion chemistry, good chargers that prevent damage to the cell by varying charging rate based on resistance and cut off charge at 4.20V are expensive. Many cheap chargers exist that rely on the cell's protection circuit to cut off charge at 4.20v and should be avoided, should a protection ciruit fail or should you ever with to use unprotected, safer chemistry 3.6-3.8V cells. The nominal voltage of these cells is slightly higher than V.in of a white LED, making them ideal for 1 cell flashlights with current regulators, or 2 (or more) cell lights with buck drivers.

IMR cells (Li-Ion rechargeables of different chemistry, usually LiMn or other Li + Mn chemistries): These are the "safe chemistry" Li-Ion rechargeables that are much more stable because of the way oxygen liberation is avoided in the chemistry. Capacity is less than that of conventional LiCo chemistry Li-Ion cells. Nominal voltage is 3.7-3.8v. Maximum safe discharge current in mA is typically 5x capacity in mAH. Lack of protection circuits on these cells requires a good charger. Over charge, over discharge and excessive discharge current will damage these cells by increasing internal resistance and reducing capacity. Best brand available as loose cells is AW IMR. Other brands typically found in tool packs, such as Molicell, are sometimes available as loose cells.

LiFePO4 cells: Safest Li chemistry. Lowest capacity. No protection circuits. Nominal voltage 3.2V. Maximum safe discharge current varies with brand but is almost always at east 5x capacity and sometimes as high as 20x capacity. As with other chemistries, the highest current capable cells typically have the lowest capacity. These cells handle abuse better than any other Li chemistry, especially rebounding from over discharge. Maximum number of recharge cycles is twice that of LiCo and LiMn cells. Best brand is A123 Li Nano Phosphate cells. Inexpensive, unbranded LiFe cells from China are widely available as loose cells. A special 3.0/3.2v cell charger with cutoff is required to avoid overcharging.

2. Intended purpose or use of the light:
Single mode lights don't have the benefit of having a low mode for long runtime and a high mode for short burts. If extended runs are desired, then choosing an emitter and a drive current for it will have to consider heatsinking and heat shedding, as well as the total desired runtime on a single charge or single set of batteries. Desire for long total runtime and/or heatshedding limitations will reduce max LED wattage that's appropriate for the light.

3. Heatsinking / Heat shedding capability:
If the light needs to be capable of being left on for extended periods, then heatsinking is very important. Heatsinks protect LEDs from thermal runaway by absorbing and then shedding heat from the LED. If the sink can't shed the heat to the environment through the host as fast as it can absorb it from the LED, then total Wattage should be limited to maximize runtime before the sink is soaked and throttling or runaway occurs.
Plastic lights have a heatsinking handicap. No running big giant emitters (XML,SST50,SST90) at full blast, at least not for more than just 1-2 minutes. You can run an XPG at full blast in short bursts until the sink is soaked. As heatsink mass increases, the amount of heat it can store before being soaked (temperature = LED runaway temp) increases.

4. Desired beam profile:
The other factor to consider is the type of beam profile you want. Do you want a narrow, focused beam that concentrates most of the light for throw, or do you want a flood light for close-range use that lights up a wide area nearby? In a fixed focus reflector, and with fairly constant power and heat profiles (i.e. same wattage as driven), a small emitter driven hard will produce better throw and a more intense hotspot, and a larger emitter will produce brighter flood and a softer hotspot.

I like this Modding 101. Even I can understand it!
(Which is why I've revived it - sorry).
It was written "some time ago" - but it's clear and concise. Anything changed since then?

Thanks.

"...[they] Carry Torches And Pass Them One To Another" Socrates ~360 BCE

Re: Old Army flashlight updated to modern technology

Originally Posted by Techjunkie

[...] I'm sorry I didn't take before and after beamshots after cleaning up the switch with 2-26 contact cleaner but before modding the rest. When I first turned it on after I cleaned the switch, I didn't think it was working until I turned it around and looked directly at the bulb. Kestrel was kind enough to provide this reference beamshot, which you can imagine as a before-shot (although I don't think this light was working even quite that well.

My apologies to Techjunkie for my 'spoof' "before" beamshot I supplied (in post #2); it isn't directly related to the light in question.
Perhaps it is related in spirit however, lol.

Re: Old Army flashlight updated to modern technology

My apologies to Techjunkie for my 'spoof' "before" beamshot I supplied (in post #2); it isn't directly related to the light in question.
Perhaps it is related in spirit however, lol.

fwiw, I've got a similar flashlight that I received during my time in the military. It is truly an awful light by today's standards! By the standards of the day, it was okay.. it used the standard bulb for two carbon/zinc cells. The reflector was marginal, the lens was cheap plastic. The switch was prone to getting flattened if you dropped the light.

On the plus side, it was fairly waterproof!

I've briefly thought about converting it to LED, but the lack of heatsinking and the need for D cells (or at least AA-to-D adapters) reduce the appeal. I may just keep the light to show people how rough life was "back in the day".